Low odor binders curable at room temperature

ABSTRACT

Topically-applied binder materials for imparting wet strength to soft, absorbent paper sheets, such as are useful as household paper towels and the like, include an epoxy-reactive polymer, such as a carboxyl-functional polymer, and an epoxy-functional polymer. These binder materials can be cured at ambient temperature over a period of days and do not impart objectionable odor to final product when wetted.

This application is a divisional of U.S. patent application Ser. No.10/893,209 filed Jul. 15, 2004, now U.S. Pat. No. 7,229,529, which is acontinuation-in-part of U.S. patent application Ser. No. 10/654,556filed Sep. 2, 2003, now U.S. Pat. No. 7,189,307.

BACKGROUND OF THE INVENTION

In the manufacture of certain bonded non-woven products, the use oftopical binders to impart added strength to the final product is wellknown. An example of such a process is disclosed in U.S. Pat. No.3,879,257 entitled “Absorbent Unitary Laminate-Like Fibrous Webs andMethod for Producing Them” and issued Apr. 22, 1975 to Gentile et al.,herein incorporated by reference. A problem associated with commerciallyavailable topical binders is that they require a highly elevated curingtemperature to impart the desired strength, which in turn requires acuring oven or equivalent apparatus. These requirements add to thecapital and manufacturing costs associated with the product. Also, somecommercially available binders can emit hazardous air pollutants, suchas formaldehyde, and the resulting product can exhibit an undesirableodor, particularly when wetted.

Therefore there is a need for a binder system that provides sufficientstrength to the product, yet does not require high temperatures andassociated equipment for curing, does not emit formaldehyde duringcrosslinking and does not produce an objectionable odor when theresulting paper product is wetted.

SUMMARY OF THE INVENTION

It now has been discovered that binder systems involving the reactionbetween an epoxy-reactive polymer and an epoxy-functional polymer, whentopically applied to a fibrous web such as a paper towel basesheet, cancure at ambient or low temperature without emitting formaldehyde andwithout imparting objectionable odors to the resulting product. The lowodor associated with the products of this invention is due to theabsence of known odor causing species, or alternatively, the presence ofknown odor-causing species in low levels, near or below the human nosedetection threshold. Odor-causing species sometimes associated withbonded nonwoven products include amines, methylamines, dimethylamines,trimethylamines, organic acids, aldehydes and malodorouscellulose-degradation products which can occur when a high temperaturecure process is required. The level of odor is usually increased whenthe product is wetted with water or other fluids, particularly fluidshaving a pH above 7.

Without being bound by theory, it is hypothesized that during curing,the epoxy groups of the epoxy-functional polymer react with theepoxy-reactive groups of the epoxy-reactive polymer to form variouslinkages, such as ester linkages when the epoxy-reactive groups arecarboxyl groups, thereby cross-linking the epoxy-reactive polymerstogether to form a durable bonded structure with wet tensile strengthpermanence. The wet tensile strength is evident even at the high pHassociated with window cleaners, which is an important property forhousehold towels. At the same time, the epoxy groups of theepoxy-functional polymer can also react with the carboxyl groups on thesurface of the cellulose fibers within the web to further strengthen theresulting structure. Other reactions may also be taking place betweenthe epoxy-functional polymer, the epoxy-reactive polymer and the fibersof the web substrate.

Surprisingly, it has been observed that curing of the binder system atambient temperature takes place over several days so that the wetstrength of the resulting product substantially increases with time. Tothe extent prior artisans have experimented with similar systems, theymay not have appreciated the prolonged curing reaction and may haveassumed that the resulting strength properties imparted to the web wereinsufficient. Although attainment of the ultimate wet strength can beaccelerated by high curing temperatures, high curing temperatures havebeen found to be unnecessary and disadvantageous as previouslymentioned.

Hence, in one aspect the invention resides in an aqueous bindercomposition comprising an unreacted mixture of an epoxy-reactive polymerand an epoxy-functional polymer, wherein the amount of theepoxy-functional polymer relative to the amount of epoxy-reactivepolymer can be from about 0.5 to about 25 weight percent on a solidsbasis.

In another aspect, the invention resides in a method of increasing thestrength of a fibrous web comprising topically applying an aqueousbinder composition to one or both outer surfaces of the web, wherein thebinder composition comprises an unreacted mixture of an epoxy-reactivepolymer and an epoxy-functional polymer.

In another aspect, the invention resides in a fibrous web or sheethaving first and second outer surfaces, wherein at least one outersurface comprises a topically-applied network of a cured bindercomposition resulting from the cross-linking reaction of anepoxy-reactive polymer and an epoxy-functional polymer. As used herein,the term “network” is used to describe any binder pattern that serves tobond the sheet together. The pattern can be regular or irregular and canbe continuous or discontinuous.

Products incorporating the fibrous webs of this invention can besingle-ply or multi-ply (two, three, or more plies). The bindercomposition can be applied to one or more surfaces of the ply or plieswithin the product. For example, a single-ply product can have one orboth surfaces treated with the binder composition. A two-ply product canhave one or both outer surfaces treated with the binder compositionand/or one or both inner surfaces treated with the binder composition.In the case of a two-ply product, it can be advantageous to have one orboth binder-treated surfaces plied inwardly in order to expose theuntreated surface(s) of the plies on the outside of the product forpurposes of hand-feel or absorbency. When the binder is applied to theinner surfaces of a multi-ply product, the binder also provides a meansof bonding the plies together. In such cases, mechanical bonding may notbe required. In the case of a three-ply product, the same options areavailable. In addition, for example, it may be desirable to provide acenter ply which is not treated with binder while the two outer pliesare treated with binder as described above.

As used herein, a “polymer” is a macromolecule consisting of at leastfive monomer units. More particularly, the degree of polymerization,which is the number of monomer units in an average polymer unit for agiven sample, can be about 10 or greater, more specifically about 30 orgreater, more specifically about 50 or greater and still morespecifically from about 10 to about 10,000.

Epoxy-reactive polymers suitable for use in accordance with thisinvention are those polymers containing functional pendant groups thatwill react with epoxy-functional molecules. Such reactive functionalgroups include carboxyl groups, anhydrides, amines, polyamides, phenolicresins, isocyanates, polymercaptans, alcohols, and others. Particularlysuitable epoxy-reactive polymers include carboxyl-functional latexemulsion polymers. More particularly, carboxyl-functional latex emulsionpolymers useful in accordance with this invention can comprise aqueousemulsion addition copolymerized unsaturated monomers, such as ethylenicmonomers, polymerized in the presence of surfactants and initiators toproduce emulsion-polymerized polymer particles. Unsaturated monomerscontain carbon-to-carbon double bond unsaturation and generally includevinyl monomers, styrenic monomers, acrylic monomers, allylic monomers,acrylamide monomers, as well as carboxyl functional monomers. Vinylmonomers include vinyl esters such as vinyl acetate, vinyl propionateand similar vinyl lower alkyl esters, vinyl halides, vinyl aromatichydrocarbons such as styrene and substituted styrenes, vinyl aliphaticmonomers such as alpha olefins and conjugated dienes, and vinyl alkylethers such as methyl vinyl ether and similar vinyl lower alkyl ethers.Acrylic monomers include lower alkyl esters of acrylic or methacrylicacid having an alkyl ester chain from one to twelve carbon atoms as wellas aromatic derivatives of acrylic and methacrylic acid. Useful acrylicmonomers include, for instance, methyl, ethyl, butyl, and propylacrylates and methacrylates, 2-ethyl hexyl acrylate and methacrylate,cyclohexyl, decyl, and isodecyl acrylates and methacrylates, and similarvarious acrylates and methacrylates.

In accordance with this invention, the carboxyl-functional latexemulsion polymer can contain copolymerized carboxyl-functional monomerssuch as acrylic and methacrylic acids, fumaric or maleic or similarunsaturated dicarboxylic acids, where the preferred carboxyl monomersare acrylic and methacrylic acid. The carboxyl-functional latex polymerscomprise by weight from about 1% to about 50% copolymerized carboxylmonomers with the balance being other copolymerized ethylenic monomers.Preferred carboxyl-functional polymers include carboxylated vinylacetate-ethylene terpolymer emulsions such as Airflex® 426 Emulsion,commercially available from Air Products Polymers, LP.

Suitable epoxy-functional polymers include water soluble,poly-functional epoxy resins. Water soluble, poly-functional epoxyresins include, but are not limited to, polymeric amine-epichlorohydrincondensation products of the type commonly used as alkaline-curing wetstrength resins for paper products. Many of these resins are describedin the text “Wet Strength Resins and Their Applications”, chapter 2,pages 14-44, TAPPI Press (1994), herein incorporated by reference. Othertypes of epoxy-functional polymers are also useful, includingepoxy-modified organoreactive silicones, glycidyl epoxy resins includingglycidyl-ether, glycidyl-ester and glycidyl amine resins, as well asaliphatic or cycloaliphatic non-glycidyl epoxy resins.

The epoxy-functional polymers commonly used as alkaline-curing wetstrength resins are made by reacting a polyamine or an amine-containingpolymer with an epoxide possessing a second functional group (typicallyan epihalohydrin such as epichlorohydrin, epibromohydrin,epifluorohydrin or epiiodohydrin, most preferably epichlorohydrin) inwater solution. The epihalorohydrin alkylates and cross-links thepolyamine to a moderate molecular weight. The cross-linking reaction isthen arrested by dilution, and/or by reducing the pH to convert aminegroups to their acid salts. The resulting polymer contains multiplefunctional groups that can partake in cross-linking reactions and alsopossesses cationic charge in water, which helps render the moleculewater soluble and thus able to be easily formulated into an aqueousemulsion or dispersion which contains polymers with epoxy-reactivefunctional groups.

When selecting an epoxy-functional polymer it is advantageous to use amulti-functional reactant possessing 4 or more pendant epoxy moietiesper molecule in order to provide sufficient cross-linking. Morespecifically, the number of pendant epoxy moieties per molecule can beabout 10 or more, more specifically about 50 or more, more specificallyabout 100 or more, more specifically from about 10 to about 2000, morespecifically from about 10 to about 1000, and still more specificallyfrom about 25 to about 1000. Particularly suitable epoxy-functionalpolymers include quaternary ammonium epoxide polymers, such aspoly(methyldiallylamine)-epichlorohydrin resin commercially available asKymene® 2064, from Hercules Inc.

In the case of a quaternary ammonium epoxide polymer as mentioned above,the epoxide groups can be converted to chlorohydrins by reaction withhydrochloric acid. The less reactive chlorohydrin form of the polymerfacilitates storage of the concentrated polymer, which can be held at apH of about 4-5, for example. Prior to use, the chlorohydrin groups canbe reconverted to epoxide groups by a reaction with alkali. The alkaliconversion of chlorohydrin groups to epoxide groups for apoly(methyldiallylamine) -epichlorohydrin resin is shown below.

The rate of reaction increases with increasing pH. For maximumefficiency, a stoichiometric amount of alkali is needed to convert allof the chlorohydrin groups to epoxide. However, an excess of alkali canaccelerate hydrolysis of the epoxide groups. The reactivation is usuallyperformed in dilute solution to avoid premature gelation, and goodstirring is essential to avoid locally excessive concentrations andconsequent gel formation.

The relative amounts of the epoxy-reactive polymer and theepoxy-functional polymer will depend on the number of functional groups(degree of functional group substitution on molecule) present on eachcomponent. In general, it has been found that properties desirable for adisposable paper towel, for example, are achieved when the level ofepoxy-reactive polymer exceeds that of the epoxy-functional polymer on adry solids basis. More specifically, on a solids basis, the amount ofepoxy-functional polymer relative to the amount of epoxy-reactivepolymer can be from about 0.5 to about 25 weight percent, morespecifically from about 1 to about 20 weight percent, still morespecifically from about 2 to about 10 weight percent and still morespecifically from about 5 to about 10 weight percent. For epoxy-reactivepolymers besides carboxyl-functional polymers, similar ranges for theweight ratios of epoxy-functional polymer to epoxy-reactive polymerwould apply.

The binder compositions of this invention can optionally contain one ormore additives that have been found to reduce “blocking” when the sheetis wound into a roll without interfering with, and often enhancingstrength, absorbency or other properties. Blocking is often a problemfor wound sheets that have been treated with topical binders, such aspaper toweling, because the binder on the sheet surface can interactwith the surface of an adjacent sheet, especially while in a rollformat, to bond the two surfaces together, resulting in blocking. Uponunwinding of the paper roll, the presence of blocking causes the sheetsto stick together and can tear or delaminate the sheet surface, causingdefects and an unusable product. Suitable anti-blocking additivesinclude: 1) chemically reactive additives, such as multifunctionalaldehydes, including glyoxal, glutaraldehyde and glyoxalatedpolyacrylamides designed to increase the level of crosslinking of thelatex polymer immediately after drying the web; 2) non-reactiveadditives, such as silicones, waxes, oils, designed to modify thesurface chemistry of at least one outer surface of the web to reduceblocking; and 3) soluble or insoluble crystals, such as sugars, talc,clay and the like, designed to reside on the surface of the binder filmand thus reduce its propensity to cause blocking to an adjacent websurface. The amount of the anti-blocking additive in the bindercomposition, on a weight percent solids basis, can be from about 1 toabout 25 percent, more specifically from about 5 to about 20 percent andmore specifically from about 10 to about 15 percent.

The effectiveness of an anti-blocking additive can be measured inaccordance with the Blocking Test (hereinafter described). Blocking Testvalues for fibrous sheets, particularly paper towels, in accordance withthis invention can be about 23 grams (force) or less, more specificallyabout 20 grams (force) or less, more specifically about 15 grams (force)or less, more specifically from about 4 to about 23 grams (force) andstill more specifically from about 4 to about 15 grams (force).

The surface area coverage of the binder composition on the fibrous webcan be about 5 percent or greater, more specifically about 30 percent orgreater, still more specifically from about 5 to about 90 percent, andstill more specifically from about 20 to about 75 percent.

Curing temperatures for the binder composition can be about 260° C. orless, more specifically about 120° C. or less, more specifically about100° C. or less, more specifically about 40° C. or less, morespecifically from about 10 to about 260° C. and still more specificallyfrom about 20 to about 120° C. It will be appreciated that although thebinder compositions of this invention can be cured at relatively lowtemperatures, the rate of curing can be accelerated at highertemperatures associated with curing conventional binders. However, suchhigher cure temperatures are not necessary with the binder compositionsof this invention.

Depending upon the curing temperature, the cross-machine directionwet/dry tensile strength ratio of the treated basesheets of thisinvention can increase about 30 percent or more, more specifically about50 percent or more, more specifically about 70 percent or more, morespecifically from about 30 to about 250 percent, more specifically fromabout 30 to about 150 percent, and still more specifically from about 40to about 130 percent when naturally aged for 14 days.

As used herein, dry machine direction (MD) tensile strengths representthe peak load per sample width when a sample is pulled to rupture in themachine direction. In comparison, dry cross-machine direction (CD)tensile strengths represent the peak load per sample width when a sampleis pulled to rupture in the cross-machine direction. Samples for tensilestrength testing are prepared by cutting a 3 inches (76.2 mm) wide×5inches (127 mm) long strip in either the machine direction (MD) orcross-machine direction (CD) orientation using a JDC Precision SampleCutter (Thwing-Albert Instrument Company, Philadelphia, Pa., Model No.JDC3-10, Serial No. 37333). The instrument used for measuring tensilestrengths is an MTS Systems Sintech 11 S, Serial No. 6233. The dataacquisition software is MTS TestWorks® for Windows Ver. 3.10 (MTSSystems Corp., Research Triangle Park, N.C.). The load cell is selectedfrom either a 50 Newton or 100 Newton maximum, depending on the strengthof the sample being tested, such that the majority of peak load valuesfall between 10-90% of the load cell's full scale value. The gaugelength between jaws is 4+/−0.04 inches (101.6+/−1 mm). The jaws areoperated using pneumatic-action and are rubber coated. The minimum gripface width is 3 inches (76.2 mm), and the approximate height of a jaw is0.5 inches (12.7 mm). The crosshead speed is 10+/−0.4 inches/min(254+/−1 mm/min), and the break sensitivity is set at 65%. The sample isplaced in the jaws of the instrument, centered both vertically andhorizontally. The test is then started and ends when the specimenbreaks. The peak load is recorded as either the “MD dry tensilestrength” or the “CD dry tensile strength” of the specimen depending onthe sample being tested. At least six (6) representative specimens aretested for each product and the arithmetic average of all individualspecimen tests is either the MD or CD tensile strength for the product.

Wet tensile strength measurements are measured in the same manner, butare only typically measured in the cross-machine direction of thesample. Prior to testing, the center portion of the CD sample strip issaturated with tap water immediately prior to loading the specimen intothe tensile test equipment. CD wet tensile measurements can be made bothimmediately after the product is made and also after some time ofnatural aging of the product. For mimicking natural aging, experimentalproduct samples are stored at ambient conditions of approximately 23° C.and 50% relative humidity for up to 15 days or more prior to testing sothat the sample strength no longer increases with time. Following thisnatural aging step, the samples are individually wetted and tested. Formeasuring samples that have been made more than two weeks prior totesting, which are inherently naturally aged, such conditioning is notnecessary.

Sample wetting is performed by first laying a single test strip onto apiece of blotter paper (Fiber Mark, Reliance Basis 120). A pad is thenused to wet the sample strip prior to testing. The pad is aScotch-Brite® brand (3M) general purpose commercial scrubbing pad. Toprepare the pad for testing, a full-size pad is cut approximately 2.5inches (63.5 mm) long by 4 inches (101.6 mm) wide. A piece of maskingtape is wrapped around one of the 4 inch (101.6 mm) long edges. Thetaped side then becomes the “top” edge of the wetting pad. To wet atensile strip, the tester holds the top edge of the pad and dips thebottom edge in approximately 0.25 inch (6.35 mm) of tap water located ina wetting pan. After the end of the pad has been saturated with water,the pad is then taken from the wetting pan and the excess water isremoved from the pad by lightly tapping the wet edge three times on awire mesh screen. The wet edge of the pad is then gently placed acrossthe sample, parallel to the width of the sample, in the approximatecenter of the sample strip. The pad is held in place for approximatelyone second and then removed and placed back into the wetting pan. Thewet sample is then immediately inserted into the tensile grips so thewetted area is approximately centered between the upper and lower grips.The test strip should be centered both horizontally and verticallybetween the grips. (It should be noted that if any of the wetted portioncomes into contact with the grip faces, the specimen must be discardedand the jaws dried off before resuming testing.) The tensile test isthen performed and the peak load recorded as the CD wet tensile strengthof this specimen. As with the dry tensile tests, the characterization ofa product is determined by the average of six representative samplemeasurements.

Similar to the CD wet tensile test described above, CD wet tensile mayalso be tested with an alternate testing fluid, particularly one havinga higher pH such as Formula 409® All-Purpose Cleaner (Clorox Company),for example, which has a pH of about 12 (11.5). With this test twoprocedural changes occur. The first change is pouring out the tap waterin the wetting pan and replacing it with 0.25 inches (6.35 mm) of thealternate testing fluid. The second change is to prepare a secondScotch-Brite brand (3M) general purpose commercial scrubbing pad asdescribed above, where one pad is used for tap water and the other isused for the alternate testing fluid. The CD wet tensile test is thenperformed exactly as described above except using the alternate pad andthe alternate testing fluid.

In addition to tensile strength, stretch, tensile energy absorbed (TEA),and slope are also reported by the MTS TestWorks® for Windows Ver. 3.10program for each sample measured both dry and wet. Stretch is reportedas a percentage and is defined as the ratio of the slack-correctedelongation of a specimen at the point it generates its peak load dividedby the slack-corrected gage length. Tensile energy absorbed is reportedin the units of grams−centimeters/centimeters squared (g−cm/cm²) and isdefined as the integral of the force produced by a specimen with itselongation up to the defined break point (65% drop in peak load) dividedby the face area of the specimen. Slope is reported in the units ofgrams (g) and is defined as the gradient of the least-squares linefitted to the load-corrected strain points falling between aspecimen-generated force of 70 to 157 grams (0.687 to 1.540 N) dividedby the specimen width.

As used herein, “bulk” is calculated as the quotient of the caliper(hereinafter defined) of a product, expressed in microns, divided by thebasis weight, expressed in grams per square meter. The resulting bulk ofthe product is expressed in cubic centimeters per gram. Caliper ismeasured as the total thickness of a stack of ten representative sheetsof product and dividing the total thickness of the stack by ten, whereeach sheet within the stack is placed with the same side up. Caliper ismeasured in accordance with TAPPI test methods T402 “StandardConditioning and Testing Atmosphere For Paper, Board, Pulp Handsheetsand Related Products” and T411 om-89 “Thickness (caliper) of Paper,Paperboard, and Combined Board” with Note 3 for stacked sheets. Themicrometer used for carrying out T411 om-89 is an Emveco 200-A TissueCaliper Tester available from Emveco, Inc., Newberg, Oreg. Themicrometer has a load of 2.00 kilo-Pascals (132 grams per square inch),a pressure foot area of 2500 square millimeters, a pressure footdiameter of 56.42 millimeters, a dwell time of 3 seconds and a loweringrate of 0.8 millimeters per second. After the caliper is measured, thetop sheet of the stack of 10 is removed and the remaining sheets areused to determine the basis weight.

The products (single-ply or multi-ply) or sheets of this invention canhave a bulk of about 11 cubic centimeters or greater per gram, morespecifically about 12 cubic centimeters or greater per gram, morespecifically about 13 cubic centimeters or greater per gram, morespecifically from about 11 to about 20 cubic centimeters per gram, andstill more specifically from about 12 to about 20 cubic centimeters pergram.

As used herein, the Blocking Test value is determined by ASTM D5170-98-Standard Test Method for Peel Strength (“T” Method) of Hook andLoop Touch Fasteners, but with the following exceptions in order toadapt the method from hook and loop testing to tissue testing (modifiedASTM section numbers are shown in parenthesis):

-   (a) Replace all references to “hook and loop touch fasteners” with    “blocked tissue samples”.-   (b) (Section 3.3) Only one calculation method is used, namely the    “integrator average” or average force over the measured distance.-   (c) (Section 4.1) No roller device is used.-   (d) (Section 6. Specimen Preparation) Replace all contents with the    following:

The level of blocking that will occur naturally over prolonged agingunder pressure in a wound roll can be simulated by conditioning thesamples in an oven under pressure. To artificially block samples, the 2sheet specimens to be blocked together are cut to 76.2±1 mm (3±0.04inches) in the cross direction by 177.8±25.4 mm (7±1 inch) in themachine direction. The specimens are then placed on a flat surface in anoven operating at 66° C. On top of the specimens is placed a lightweightpolycarbonate plate. On top of the polycarbonate plate, centered on thesample strips, is placed an iron block weighing approximately 11,800 gand having a bottom face area of 10.2 cm×10.2 cm. The samples are storedin the oven under the applied weight for 1 hour. When the samples areremoved from the oven, they are allowed to equilibrate under noadditional weight for at least 4 hours in standard TAPPI conditions (25°C. and 50% relative humidity) prior to conducting the blocking test.

-   (e) (Section 8. Procedure) Replace all contents with the following:

“Separate the top and bottom sheet of the specimen along the CD (3 inch)edge. Peel back approximately 51 mm (2 inches) of the top and bottomsheets in the machine direction. Position the clamps of the tensiletester so they are 25.4±1 mm (1±0.04 inches) apart. Place the free endsof the specimen to be tested in the clamps of the tensile tester, withthe specimen tail facing away from the frame. The point of specimenseparation should be approximately centered between the clamps andaligned approximately parallel to the clamps. For the integratorcalculation, set up the software to begin averaging after 25.4 mm (1inch) of separation and end averaging after 88.9 mm (3.5 inches) ofseparation. The software should be set up to separate the sample over atotal of 101.6 mm (4 inches).”

-   (f) (Section 9. Calculation) Omit all but 9.2.-   (g) (Section 10. Report) Replace all contents with the following:

“Report the integrator average for each specimen.”

-   (h) (Section 11.1) Replace all contents with the following:

“At least 5 specimens should be tested for a reliable sample average.”

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one photograph executed incolor. Copies of this patent with color photograph(s) will be providedby the Office upon request and payment of the necessary fee.

FIG. 1 is a schematic flow diagram of a process for topically applying abinder or binders to a paper web in accordance with this invention.

FIG. 2A is a magnified color photograph of a surface of a stained wetlaid paper towel basesheet, made in accordance with Example 10 herein,onto which the binder material has been printed in accordance with thisinvention, illustrating the pattern of the spaced-apart binder depositson this side of the sheet. The actual area of the sheet shown in thephotograph (and also in the photographs of FIGS. 2B, 3A and 3B) is anarea measuring about 3.43 millimeters by about 2.74 millimeters.

FIG. 2B is a color photograph of the opposite side of the paper towelbasesheet of FIG. 2A, illustrating the pattern of spaced-apart binderdeposits on this side of the sheet.

FIG. 2C is a color cross-sectional photograph of the paper towelbasesheet of FIG. 2A, further illustrating the nature of the deposits.Although not shown, some of the deposits extend deeper into the sheet asa result of periodic “deep dot” gravure cells that deposit more bindermaterial onto the surface of the sheet than most of the other gravurecells.

FIG. 3A is a color photograph of a surface of a stained paper towelbasesheet in accordance with this invention, made in accordance withExample 13 herein, wherein the binder material has been sprayed ontoboth surfaces of the sheet.

FIG. 3B is a color photograph of the opposite side of the basesheet ofFIG. 3A, illustrating the binder material deposits which are also theresult of spraying.

FIG. 3C is a color cross-sectional photograph of the basesheet of FIG.3A, further illustrating the nature of the binder deposits.

FIG. 4 is a plot of the CD wet strength as a function of time for papertowel basesheets made in accordance with Examples 1-4 described below,illustrating the effect of curing temperature on one of the bindermaterials of this invention.

FIG. 5 is a plot, similar to that of FIG. 4, of the CD wet strength as afunction of time for paper towel basesheets made in accordance withExamples 1, 5, 6 and 7 described below, illustrating the effect ofcuring temperature on a different binder material of this invention.

FIG. 6 is a plot, similar to FIGS. 4 and 5, of the CD wet strength as afunction of time for paper towel basesheets made in accordance withExamples 1, 8, 9 and 10 described below, illustrating the effect ofcuring temperature on a different binder material of this invention.

FIG. 7 is a plot of the CD wet strength as a function of time for thepaper towel basesheets cured at 38° C. in accordance with Examples 1, 4,7 and 10, illustrating the effect of varying levels of epoxy-functionalpolymer (Kymene® 2064) at constant curing temperature.

FIG. 8 is a plot, similar to that of FIG. 7, of the CD wet strength as afunction of time for the paper towel basesheets cured at 149° C. inaccordance with Examples 1, 3, 6 and 9, further illustrating the effectof varying levels of epoxy-functional polymer at a different constantcuring temperature.

FIG. 9 is a plot similar to that of FIGS. 7 and 8, but for a curingtemperature of 260° C.

FIG. 10 is plot of the CD wet strength as a function of time for papertowel basesheets made in accordance with Examples 1 and 11, illustratingthe improvement in wet strength using the binder material of thisinvention in the presence of glyoxal.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, shown is a method of applying a topical bindermaterial to a previously-formed basesheet or web. The binder materialcan be applied to one or both sides of the web. For wet laid basesheets,at least one side of the web is thereafter creped. In general, for mostapplications, the basesheet or web will only be creped on one side afterthe binder materials are applied. It should be understood, however, thatin some situations it may be desirable to crepe both sides of the web.Alternatively, nonwoven manufacturing processes which may not contain acreping step, such as air-laid papermaking processes, for example, mayalso utilize the low odor binder of the present invention for impartingstructural integrity to the web. In such cases, post-treatment withtopical binder material is optional.

In all cases, prior to applying the binder material to the web, theepoxy-reactive polymer and the epoxy-functional polymer must be mixedtogether and the epoxy-functional polymer must be reactivated by theaddition of a base to increase the pH. In their stable, less reactiveform, the epoxy-functional groups within the epoxy-functional polymerare in a halohydrin form and maintained as such by a low pH. Suitably,the pH can be about 4 or 5 prior to activation. Once the pH is raised,such as to a level of 11 or higher, the halohydrin form returns to theactive epoxy form. Once this occurs, the binder material must be appliedto the web in a relatively short time (less than about 3 hours) formaximum binder efficiency. Consequently, the binder material may beprepared in different ways, but a convenient method of preparation is todilute the epoxy-functional polymer with water and add a base, such assodium hydroxide, to raise the pH above 11 and activate the epoxygroups. Thereafter, the activated epoxy-functional polymer is blendedwith the epoxy-reactive polymer and other components and the resultingblended binder formulation is applied to the fibrous web, such as byprinting, spraying, coating, foaming, size pressing or other means.Depending upon the reactivity of the activated epoxy-functional polymer,the elapsed time between blending of the binder composition and itsapplication to the web can be less than a day, more specifically 12hours or less, more specifically 2 or 3 hours or less, and still morespecifically about 30 minutes or less.

Returning to FIG. 1, a fibrous web 10 made according to any suitablewet-laying or air-laying process is passed through a first bindermaterial application station 12. Station 12 includes a nip formed by asmooth rubber press roll 14 and a patterned rotogravure roll 16.Rotogravure roll 16 is in communication with a reservoir 18 containing afirst binder material 20. The rotogravure roll applies the bindermaterial to one side of web in a pre-selected pattern.

Web 10 is then contacted with a heated roll 22 after passing a roll 24.The heated roll 22 serves to at least partially dry the web. The heatedroll can be heated to a temperature, for instance, up to about 121° C.and particularly from about 82° C. to about 104° C. In general, the webcan be heated to a temperature sufficient to dry the web and evaporateany water. During the time the web is heated, some curing of the binderon the sheet may occur.

It should be understood, that the besides the heated roll 22, anysuitable heating device can be used to dry the web. For example, in analternative embodiment, the web can be placed in communication with athrough-air dryer or an infra-red heater in order to dry the web. Otherheating devices can include, for instance, any suitable convective oven,microwave oven or other suitable electromagnetic wave energy source.

From the heated roll 22, the web 10 can be advanced by pull rolls 26 toa second binder material application station generally 28. Station 28includes a transfer roll 30 in contact with a rotogravure roll 32, whichis in communication with a reservoir 34 containing a second bindermaterial 36. Similar to station 12, second binder material 36 is appliedto the opposite side of web 10 in a pre-selected pattern. Once thesecond binder material is applied, web 10 is adhered to a creping rollor drum 38 by a press roll 40. The web is carried on the surface of thecreping roll for a distance and then removed therefrom by the action ofa creping blade 42. The creping blade performs a controlled patterncreping operation on the second side of the paper web.

In accordance with the present invention, the second binder material 36is selected such that the web 10 can be adhered to and creped from thecreping drum 38. For example, in accordance with the present invention,the creping drum can be maintained at a temperature of between 66° C.and 121° C. Operation outside of this range is also possible. In oneembodiment, for example, the creping drum 38 can be at 104° C.Alternatively, the creping drum need not be heated or only heated to arelatively low temperature.

Once creped, the paper web 10 is pulled through a drying station 44.Drying station 44 can include any form of a heating unit, such as anoven energized by infrared heat, microwave energy, hot air or the like.Alternatively, the drying station may comprise other drying methods suchas photo-curing, UV-curing, corona discharge treatment, electron beamcuring, curing with reactive gas, curing with heated air such asthrough-air heating or impingement jet heating, infrared heating,contact heating, inductive heating, microwave or RF heating, and thelike. The dryer may also include a fan to blow air onto the moving web.Drying station 44 may be necessary in some applications to dry the weband/or cure the first and second binder materials. Depending upon thebinder materials selected, however, in other applications the dryingstation may not be needed.

The amount that the paper web is heated within the drying station 44 candepend upon the particular binder materials used, the amount of bindermaterials applied to the web, and the type of web used. In someapplications, for instance, the paper web can be heated using a gasstream such as air at a temperature of about 266° C. in order to curethe binder materials. When using low cure temperature binder materials,on the other hand, the gas can be at a temperature lower than about 132°C. and particularly lower than about 121° C. In an alternativeembodiment, the drying station 44 is not used to cure the bindermaterial applied to the web. Instead, the drying station is used to drythe web and to drive off any water present in the web. In thisembodiment, the web can be heated to temperatures sufficient toevaporate water, such as to a temperature of from about 90 to about 120°C. In other embodiments, room temperature air (20-40° C.) may besufficient to dry the web. In still other embodiments, the dryingstation may be bypassed or removed from the process altogether.

Once passed through drying station, web 10 can be wound into a roll ofmaterial 46 for subsequent conversion into the final product. In otherembodiments, the web may proceed directly into further convertingoperations to result in the final product without being wound into anintermediate roll.

FIGS. 2A-C and 3A-C, as previously mentioned, are photographs ofproducts of this invention made in accordance with the examples. Thesephotographs show the size dimension, spacing, area coverage andpenetration of two potential embodiments. In order to delineate thelocation of the bonding material in the fibrous web, the samples weretreated with DuPont Fiber Identification Stain #4 (Pylam ProductsCompany, Inc., Garden City, N.Y.), a blend of dyes commonly used in thetextile industry for fiber identification.

FIG. 4 is a plot of the CD wet tensile strength in water as a functionof aging time prior to testing, illustrating the wet strengthdevelopment with 2.5% Kymene® 2064 addition and varying curetemperatures. It is evident from this plot that the initial CD wettensile can be increased by curing at high temperatures, but after thesamples have aged for 15 days all CD wet tensile values were similar,irregardless of the initial curing temperature.

FIG. 5 is a plot of the CD wet tensile strength in water as a functionof aging time prior to testing, illustrating the wet strengthdevelopment with 5% Kymene® 2064 addition and varying cure temperatures.A similar trend of wet tensile development with aging time, as wasdemonstrated in FIG. 4, is also evident in this plot.

FIG. 6 is a plot of the CD wet tensile strength in water as a functionof aging time prior to testing, illustrating the wet strengthdevelopment with 10% Kymene® 2064 addition and varying curetemperatures. A similar trend of wet tensile development with agingtime, as was demonstrated in FIGS. 4 and 5, is also evident in thisplot.

FIG. 7 is a plot of the CD wet tensile strength in water as a functionof aging time prior to testing, illustrating the CD wet tensile strengthcured at 38° C. with varying Kymene® 2064 addition levels. From thisplot the level of Kymene® 2064 in the binder recipe does not appear toimpact the initial wet tensile values, but does impact the aged wettensile values, with the higher level of Kymene® 2064 resulting in ahigher level of wet tensile strength.

FIG. 8 is a plot of the CD wet tensile strength in water as a functionof aging time prior to testing, illustrating the CD wet tensile strengthcured at 149° C. with varying Kymene® 2064 addition levels. From thisplot the level of Kymene® 2064 in the binder recipe does not appear toimpact the initial wet tensile values, but does impact the aged wettensile values, with the higher level of Kymene® 2064 resulting in ahigher level of wet tensile strength.

FIG. 9 is a plot of the CD wet tensile strength in water as a functionof aging time prior to testing, illustrating the CD wet tensile strengthcured at 260° C. with varying Kymene® 2064 addition levels. From thisplot the level of Kymene® 2064 in the binder recipe does not appear toimpact the initial wet tensile values, but does impact the aged wettensile values, with the higher level of Kymene® 2064 resulting in ahigher level of wet tensile strength.

FIG. 10 is plot of the CD wet tensile strength in water as a function ofaging time prior to testing, illustrating the improvement in wetstrength using the binder material of this invention in the presence ofglyoxal.

EXAMPLES Example 1 Comparative

A tissue machine was used to produce a layered, uncrepedthrough-air-dried (UCTAD) basesheet generally as described in thefollowing U.S. patents: U.S. Pat. No. 5,607,551, issued Mar. 4, 1997 toFarrington et al.; U.S. Pat. No. 5,672,248 issued Sep. 30, 1997 to Wendtet al.; and U.S. Pat. No. 5,593,545 issued Jan. 14, 1997 to Rugowski etal., all of which are hereby incorporated by reference. Aftermanufacture on the tissue machine, the UCTAD basesheet was printed oneach side with a latex-based binder. The binder-treated sheet wasadhered to the surface of a Yankee dryer to re-dry the sheet andthereafter the sheet was creped and thermally cured. The resulting sheetwas tested for physical properties immediately after manufacture andthen periodically during a 2 week period to monitor development ofstrength properties after natural aging at room temperature (about 23°C.) and humidity (about 50% relative humidity).

More specifically, the basesheet was made from a stratified fiberfurnish containing a center layer of fibers positioned between two outerlayers of fibers. Both outer layers of the UCTAD basesheet contained100% northern softwood kraft pulp and about 6.5 kilograms (kg)/metricton (Mton) of dry fiber of a debonding agent, ProSoft® TQ1003 (Hercules,Inc.). Combined, the outer layers comprised 50% of the total fiberweight of the sheet (25% in each layer). The center layer, whichcomprised 50% of the total fiber weight of the sheet, was also comprisedof northern softwood kraft pulp. The fibers in this layer were alsotreated with 6.5 kg/Mton of ProSoft® TQ1003 debonder.

The machine-chest furnish containing the chemical additives was dilutedto approximately 0.2 percent consistency and delivered to a layeredheadbox. The forming fabric speed was approximately 445 meters perminute. The resulting web was then rush-transferred to a transfer fabric(Voith Fabrics, 807) traveling 17% slower than the forming fabric usinga vacuum box to assist the transfer. At a second vacuum-assistedtransfer, the web was transferred and wet-molded onto the throughdryingfabric (Voith Fabrics, t1203-9). The web was dried with athrough-air-dryer resulting in a basesheet with an air-dry basis weightof approximately 56 grams per square meter (gsm).

The resulting sheet was fed to a gravure printing line, similar to thatshown in FIG. 1, traveling at about 200 feet per minute (61 meters perminute) where a latex binder was printed onto the surface of the sheet.The first side of the sheet was printed with a bonding formulation usingdirect rotogravure printing. Then the printed web passed over a heatedroll with a surface temperature of approximately 104° C. to evaporatewater. Next, the second side of the sheet was printed with the bondingformulation using a second direct rotogravure printer. The sheet wasthen pressed against and doctored off a rotating drum, which had asurface temperature of approximately 104° C. Finally the sheet was driedand the bonding material cured using air heated to about 260° C. andwound into a roll.

Thereafter the print/print/creped sheet was removed from the roll andtested for basis weight, caliper and tensile strength.

The latex binder in this example was a vinyl acetate ethylene copolymer,Airflex® EN1165, which was obtained from Air Products and Chemicals,Inc. of Allentown, Pa. Approximately 5.7% by weight. Airflex® EN1165 wasapplied to the sheet.

The bonding formulation contained the following ingredients, listed intheir order of addition.

1. Airflex ®EN1165 (52% solids) 10,500 g 2. Defoamer (Nalco 7565) 54 g3. Water 3,400 g 4. LiCl solution tracer (10% solids) 50 g 5. CitricAcid Catalyst (10% solids) 540 g 6. Natrosol 250MR, Hercules (2% solids)1,200 g

The amount of Natrosol thickener added to the formulation was based onrequirements to achieve approximately 120 centipoise (cps) viscosity.All ingredients were added to the EN1165 latex emulsion under mildagitation. After all ingredients had been added, the print fluid wasallowed to mix for approximately 15 minutes prior to use in the gravureprinting operation.

Lithium Chloride (LiCl) salt was added to the bonding formulation as atracer to enable latex addition level to be analyzed using atomicabsorption spectroscopy. An amount of LiCl no less than 250 parts permillion (ppm) was added in the bonding formulation to ensure accuratedetection measurement. The LiCl granules were dissolved in water andthen added to the bonding formulation under agitation. After applyingthe bonding formulation to a basesheet, a sample of the bondingformulation and also a sample of the bonded sheet were collected foranalysis.

The bonding formulation and bonded sheet were analyzed using atomicabsorption spectroscopy to determine the percentage of latex add-on.First a calibration curve of absorbance vs. lithium concentration in ppmwas created with standard LiCl solutions in water. The bondingformulations and bonded sheet were analyzed with atomic absorptionspectroscopy after undergoing a series of combustion and waterextraction steps to capture all lithium ions present in the respectivesamples. The weights of LiCl in the bonding formulation and bonded sheetsamples were obtained by comparing their atomic absorbance values to theLiCl calibration curve. The concentration of LiCl in the bondingformulation was calculated, and then the weight of LiCl in each bondedsheet sample was converted into the amount of bonding formulation(W_(t)(BF)) applied to the sheet based on the LiCl content in thebonding formulation. Since the total solids content of the bondingformulation, S_(T), and latex solids content, S_(L), in the total solidsare known, the percent of latex solids add-on (Latex %) can becalculated using the following equation:

${{Latex}\mspace{14mu}\%} = {\frac{{W_{t}({BF})} \times S_{T} \times S_{L}}{W_{t}\mspace{11mu}({Sample})} \times 100}$where W_(t)(BF) is the weight of bonding formulation applied to thesheet in milligrams (mg), W_(t)(Sample) is the weight of bonded sheet inmg, S_(T) is the weight percent content of total solids in the bondingformulation, and S_(L) is the weight percent of latex solids in thetotal solids.

The amount of Airflex® EN1165 latex applied to the sheet wasapproximately 5.7% by weight.

The viscosity of the print fluid was 118 cps, when measured at roomtemperature using a viscometer (Brookfield® Synchro-lectric viscometerModel RVT, Brookfield Engineering Laboratories Inc. Stoughton, Mass.)with a #1 spindle operating at 20 rpm. The oven-dry solids of the printfluid was 36.9 weight percent. The print fluid pH was 3.7.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and caliper shortly after manufacture. The tensile strengthproperties were also tested periodically over the 15 days followingmanufacture.

Example 2 Invention

A single-ply bonded sheet was produced as described in Example 1, exceptthe binder recipe in this example contained a carboxylated vinylacetate-ethylene terpolymer, Airflex® 426, which was obtained from AirProducts and Chemicals, Inc. of Allentown, Pa. The latex binder additionwas measured using atomic absorption.

The bonding formulation for this example was prepared as two separatemixtures, called the “latex” and “reactant”. The “latex” materialcontained the epoxy-reactive polymer and the “reactant” was theepoxy-functional polymer. The procedure calls for each mixture to bemade up independently, and then combined together prior to use. Afterthe latex and reactant mixtures were combined, the appropriate amount of“thickener” (Natrosol solution) was added to adjust viscosity. The“latex” and “reactant” mixtures contained the following ingredients,listed in their order of addition.

Latex 1. Airflex ®426 (62.7% solids) 8,555 g 2. Defoamer (Nalco 7565) 50g 3. Water 4,377 g 4. LiCl solution tracer (10% solids) 50 g Reactant 1.Kymene ® 2064 (20% solids) 673 g 2. Water 1,000 g 3. NaOH (10% solution)350 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture.

Thickener 1. Natrosol 250MR, Hercules (2% solids) 1,200 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer(epoxy-reactive polymer) was about 2.5%.

The viscosity of the print fluid was 110 cps, when measured at roomtemperature using a viscometer (Brookfield® Synchro-lectric viscometerModel RVT, Brookfield Engineering Laboratories Inc. Stoughton, Mass.)with a #1 spindle operating at 20 rpm. The oven-dry solids of the printfluid was 34.5 weight percent. The print fluid pH was 5.2.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and caliper shortly after manufacture. The tensile strengthproperties were also tested periodically over the 15 days followingmanufacture. The latex binder addition was measured using atomicabsorption. Approximately 5.3% by weight. Airflex® 426 was applied tothe sheet.

Example 3 Invention

A single-ply bonded sheet was produced as described in Example 2, exceptthe cure air temperature was about 149° C. The resulting single-plysheet was tested for tensile strength, basis weight and caliper shortlyafter manufacture. The tensile strength properties were also testedperiodically over the 15 days following manufacture. The latex binderaddition was measured using atomic absorption. Approximately 5.5% byweight Airflex® 426 was applied to the sheet.

Example 4 Invention

A single-ply bonded sheet was produced as described in Example 2, exceptthere was no additional heating of the cure air. The temperature of thecure air was approximately 38° C. The resulting single-ply bonded sheetwas tested for tensile strength, basis weight and caliper shortly aftermanufacture. The tensile strength properties were also testedperiodically over the 15 days following manufacture. The latex binderaddition was measured using atomic absorption. Approximately 5.1% byweight Airflex® 426 was applied to the sheet.

Example 5 Invention

A single-ply bonded sheet was produced as described in Example 2, butusing a different binder recipe. The ingredients of the “latex”,“reactant” and “thickener” used for Examples 5-7 are listed below.

Latex 1. Airflex ®426 (62.7% solids) 8,555 g 2. Defoamer (Nalco 7565) 48g 3. Water 2,344 g 4. LiCl solution tracer (10% solids) 48 g Reactant 1.Kymene ® 2064 (20% solids) 1,356 g 2. Water 2,000 g 3. NaOH (10%solution) 700 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture.

Thickener 1. Natrosol 250MR, Hercules (2% solids) 600 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer was5.0%.

The viscosity of the print fluid was 122 cps, when measured at roomtemperature using a viscometer (Brookfield® Synchro-lectric viscometerModel RVT, Brookfield Engineering Laboratories Inc. Stoughton, Mass.)with a #1 spindle operating at 20 rpm. The oven-dry solids of the printfluid was 36.7 weight percent. The print fluid pH was 5.4.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and caliper shortly after manufacture. The tensile strengthproperties were also tested periodically over the 15 days followingmanufacture. The latex binder addition was measured using atomicabsorption. Approximately 4.8% by weight. Airflex® 426 was applied tothe sheet.

Example 6 Invention

A single-ply bonded sheet was produced as described in Example 5, exceptthe cure air temperature was about 149° C. The resulting single-plybonded sheet was tested for tensile strength, basis weight and calipershortly after manufacture. The tensile strength properties were alsotested periodically over the 15 days following manufacture. The latexbinder addition was measured using atomic absorption. Approximately 5.0%by weight Airflex® 426 was applied to the sheet.

Example 7 Invention

A single-ply bonded sheet was produced as described in Example 5, exceptthere was no additional heating of the cure air. The temperature of thecure air was approximately 38° C. The resulting single-ply bonded sheetwas tested for tensile strength, basis weight and caliper shortly aftermanufacture. The tensile strength properties were also testedperiodically over the 15 days following manufacture. The latex binderaddition was measured using atomic absorption. Approximately 5.2% byweight Airflex® 426 was applied to the sheet.

Example 8 Invention

A single-ply bonded sheet was produced as described in Example 2, butusing a different binder recipe. The ingredients of the “latex”,“reactant” and “thickener” used for Examples 8-10 are listed below.

Latex 1. Airflex ®426 (62.7% solids) 8,560 g 2. Defoamer (Nalco 7565) 49g 3. Water 1,800 g 4. LiCl solution tracer (10% solids) 54 g Reactant 1.Kymene ® 2064 (20% solids) 2,712 g 2. Water 2,301 g 3. NaOH (10%solution) 1,400 g

After the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture.

Thickener 1. Natrosol 250MR, Hercules (2% solids) 0 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer was10%.

The viscosity of the print fluid was 155 cps, when measured at roomtemperature using a viscometer (Brookfield® Synchro-lectric viscometerModel RVT, Brookfield Engineering Laboratories Inc. Stoughton, Mass.)with a #1 spindle operating at 20 rpm. The oven-dry solids of the printfluid was 36.2 weight percent. The print fluid pH was 6.7.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and caliper shortly after manufacture. The tensile strengthproperties were also tested periodically over the 15 days followingmanufacture. The latex binder addition was measured using atomicabsorption. Approximately 4.5% by weight. Airflex® 426 was applied tothe sheet.

Example 9 Invention

A single-ply bonded sheet was produced as described in Example 8, exceptthe cure air temperature was about 149° C. The resulting single-plybonded sheet was tested for tensile strength, basis weight and calipershortly after manufacture. The tensile strength properties were alsotested periodically over the 15 days following manufacture. The latexbinder addition was measured using atomic absorption. Approximately 4.1%by weight Airflex® 426 was applied to the sheet.

Example 10 Invention

A single-ply bonded sheet was produced as described in Example 8, exceptthere was no additional heating of the cure air. The temperature of thecure air was approximately 38° C. The resulting single-ply bonded sheetwas tested for tensile strength, basis weight and caliper shortly aftermanufacture. The tensile strength properties were also testedperiodically over the 15 days following manufacture. The latex binderaddition was measured using atomic absorption. Approximately 4.6% byweight Airflex® 426 was applied to the sheet.

Example 11 Invention

A single-ply bonded sheet was produced as described in Example 2, butusing a different binder recipe which also incorporated glyoxal as acrosslinking agent in the latex formulation. The temperature of the cureair was approximately 38° C. The ingredients of the “latex”, “reactant”and “thickener” are listed below.

Latex 1. Airflex ®426 (62.7% solids) 8,555 g 2. Defoamer (Nalco 7565) 48g 3. Water 1,000 g 4. LiCl solution tracer (10% solids) 51 g 5. Glyoxal(40% solids) 1,349 g Reactant 1. Kymene ® 2064 (20% solids) 1,354 g 2.Water 2,004 g 3. NaOH (10% solution) 700 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture.

Thickener 1. Natrosol 250MR, Hercules (2% solids) 300 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer was5.0% and the weight percent ratio of glyoxal based on carboxylicacid-functional polymer was 10%.

The viscosity of the print fluid was 118 cps, when measured at roomtemperature using a viscometer (Brookfield® Synchro-lectric viscometerModel RVT, Brookfield Engineering Laboratories Inc. Stoughton, Mass.)with a #1 spindle operating at 20 rpm. The oven-dry solids of the printfluid was 40.4 weight percent. The print fluid pH was 5.3.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and caliper shortly after manufacture. The tensile strengthproperties were also tested periodically over the 15 days followingmanufacture. The latex binder addition was measured using atomicabsorption. Approximately 6.1% by weight. Airflex® 426 was applied tothe sheet.

The test results from Examples 1-11 are summarized in Table 1 below.

TABLE 1 Test MD Tensile MD Stretch MD TEA MD Slope CD Tensile CD StretchCD TEA CD Slope Example Day g/76.2 mm % g*cm/sq. cm g g/76.2 mm %g*cm/sq. cm g 1 0 1459 32.1 22.5 2075 1184 14.0 12.4 7464 15 1379 33.021.2 1763 1155 14.2 12.4 7991 2 0 1614 33.9 26.4 2233 1404 14.2 14.98809 15 1720 33.9 26.9 1984 1363 14.8 15.6 8935 3 0 1603 39.0 29.3 17901399 14.4 15.0 8596 1 — — — — — — — — 3 — — — — — — — — 6 1611 42.9 30.21272 1454 16.5 18.9 9009 8 — — — — — — — — 10 — — — — — — — — 15 155438.3 25.9 1373 1383 14.7 16.0 9953 4 0 1532 46.1 32.4 1471 1506 14.617.0 9644 15 1578 47.4 32.4 1127 1516 15.0 17.9 10313 5 0 1671 34.1 26.82111 1312 15.2 15.0 7751 1 — — — — — — — — 4 — — — — — — — — 5 1803 42.132.7 1612 1450 15.6 17.4 8875 7 — — — — — — — — 11 — — — — — — — — 151784 32.5 26.5 2068 1464 15.6 17.9 8998 6 0 1524 40.6 28.7 1473 125415.7 15.3 7871 1 — — — — — — — — 4 — — — — — — — — 5 1673 42.0 30.5 15171430 15.1 16.6 9212 7 — — — — — — — — 11 — — — — — — — — 15 1742 37.928.3 1528 1406 14.9 16.2 8800 7 0 1531 50.3 32.6 1088 1348 16.4 17.58547 1 — — — — — — — — 4 — — — — — — — — 5 1532 47.0 30.7 1249 1606 15.319.0 9784 7 — — — — — — — — 11 — — — — — — — — 15 1799 45.9 34.9 13551594 14.3 17.5 10237 8 0 1665 33.4 26.9 2510 1389 13.5 13.7 8526 15 157132.9 24.7 1843 1288 14.5 14.4 9019 9 0 1673 40.4 31.2 1842 1439 14.716.2 8896 1 — — — — — — — — 3 — — — — — — — — 6 1779 40.1 31.3 1649 156614.6 17.6 10162 8 — — — — — — — — 10 — — — — — — — — 15 1802 39.7 30.61447 1472 15.7 18.2 9576 10 0 1509 46.4 32.7 1494 1417 15.4 16.9 8691 151633 45.2 32.3 1273 1479 15.5 18.1 9778 11 0 1623 43.5 30.1 1361 151613.8 15.8 9465 15 1618 41.5 29.5 1452 1479 12.6 14.1 10462 CD WetTensile Basis Test CD Wet Tensile Water CD Wet Stretch Wet/Dry Formula409(pH 11.5) Weight Example Day g/76.2 mm % % g/76.2 mm gsm 1 0 699 12.559 — 67.2 15 698 12.5 60 676 — 2 0 575 10.0 41 — 68.7 15 566 9.7 42 423— 3 0 366 8.5 26 — 69.6 1 456 9.9 — — — 3 573 8.2 — — — 6 550 9.0 38 — —8 537 9.2 — — — 10 573 8.2 — — — 15 520 9.5 38 403 — 4 0 278 6.5 18 —75.3 15 548 9.0 36 446 — 5 0 562 12.4 43 — 68.9 1 606 11.0 — — — 4 66410.5 — — — 5 637 10.4 44 — — 7 694 10.2 — — — 11 682 10.0 — — — 15 67510.2 46 507 — 6 0 329 9.0 26 — 71.6 1 469 10.5 — — — 4 529 10.3 — — — 5576 9.1 40 — — 7 572 9.7 — — — 11 556 9.3 — — — 15 559 9.7 40 447 — 7 0223 6.8 17 — 74.7 1 507 9.7 — — — 4 576 10.1 — — — 5 572 9.6 36 — — 7577 9.1 — — — 11 593 8.6 — — — 15 645 9.1 40 477 — 8 0 654 10.7 47 —69.6 15 731 10.4 57 543 — 9 0 376 7.9 26 — 71.9 1 497 9.8 — — — 3 6008.6 — — — 6 637 9.3 41 — — 8 677 10.0 — — — 10 653 10.0 — — — 15 66610.4 — 506 — 10 0 205 5.6 14 — 76.4 15 674 10.2 46 498 — 11 0 526 8.5 35— 68.6 15 909 9.0 61 521 —

The data in Table 1 demonstrates the ability of the inventive binder todevelop wet tensile strength without the need of the high temperaturethermal curing required for the control binder (Example 1). The level ofdry tensile, stretch and TEA of the inventive binder was equivalent orimproved versus the control for many codes.

Example 12 Invention

A single-ply, one-side bonded sheet was produced by a spray applicationof a low odor, room temperature-curing bonding formulation.Specifically, an untreated UCTAD tissue basesheet was manufactured asdescribed in Example 1. The basesheet was then cut into 25.4 cm by 33 cmsamples (with the long dimension in the machine direction of the web)for purposes of spray application of the bonding formulation. Theingredients of the “latex” and “reactant” used for Examples 12 and 13are listed below.

Latex 1. Airflex ®426 (62.7% solids) 400 g 2. Water 231 g Reactant 1.Kymene ® 2064 (20% solids) 64 g 2. Water 95 g 3. NaOH (10% solution) 33g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture. After mixing for 5 minutes, a 246 gram sample was removed anddiluted with water to produce the final bonding formulation.

Dilution Water 1. Water (added to 246 grams of above mixture) 654 g

After the dilution water had been added, the bonding formulation wasallowed to mix for approximately 5 minutes prior to use in the sprayingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer wasabout 5.0%. The solids content of the bonding formulation wasapproximately 8.4%.

The bonding formulation was sprayed onto one side of the basesheet usingan air pressurized spray. The spray nozzle was a TEEJET model 8001-E andoperated at an air pressure of 100 pounds per square inch gauge (psig).The nozzle was approximately 22 centimeters (cm) from the substrateduring application. After application of the bonding formulation, thesheet was dried using a hot air oven (Mathis Type LTV 51793, Concord,N.C.) operating at 100° C. for 30 seconds. The dried sheet was thenweighed to determine bonding formulation add-on and finished basisweight. Bonded samples were then naturally aged for 14 days at roomtemperature (about 23° C.) and humidity (about 50% relative humidity)prior to measuring the tensile strength properties.

Example 13 Invention

A single-ply, two-side bonded sheet was produced by spray application ofa low odor, room temperature-curing bonding formulation. Specifically,an UCTAD tissue basesheet was prepared as described in Example 12. Thebonding formulation of Example 12 was also used.

The bonding formulation was sprayed onto one side of the basesheet usingan air pressurized spray. After application of the bonding formulation,the sheet was dried using a hot air oven operating at 100° C. for 30seconds. The same bonding formulation was then applied to thenon-treated side of the dried sheet and the sheet was again dried usinga hot air oven for an additional 30 seconds. After the second dryingstep, the sheet was weighed to determine bonding formulation add-on andfinished basis weight. Bonded samples were then naturally aged for 14days at room temperature (about 23° C.) and humidity (about 50% relativehumidity) before testing for tensile strengths.

The test results from Examples 12 and 13 appear in Table 2 below.Reported values are the average of three representative samples ratherthan six.

TABLE 2 Basesheet Air Dry Wt. Oven Dry Wt. Basis Weight Sprayed # Add-onExample g g gsm Sides Sprayed Dry Wt. g % 12 4.83 4.54 54.1 1 4.81 6.013 4.88 4.60 54.9 2 5.13 11.4 MD Tensile MD Stretch MD TEA MD Slope CDTensile CD Stretch CD TEA CD Slope Example g/76.2 mm % g*cm/sq. cm gg/76.2 mm % g*cm/sq. cm g 12 5066 17.6 53.2 20036 4100 9.9 24.5 14711 1310206 18.1 52.2 19889 7458 10.1 22.9 15208 CD Wet Tensile Water CD WetStretch Wet/Dry CD Wet Tensile Formula Example g/76.2 mm % % 409(pH11.5) g/76.2 mm 12 1477 5.8 36 1015 13 3281 7.5 44 2584

Table 2 demonstrates the ability of the inventive binder to improve boththe dry and wet tensile properties of a web when applied via sprayapplication to one or two sides of the material. Strength development isachieved without the use of a high temperature cure step.

Example 14 Comparative for Examples 15-18

A single-ply bonded sheet was produced generally as described inExample 1. After manufacture on the tissue machine, the UCTAD basesheetwas printed on each side with a latex-based binder. The binder-treatedsheet was adhered to the surface of a Yankee dryer to re-dry the sheetand thereafter the sheet was creped and wound onto a roll without anyadditional thermal curing. The resulting sheet was tested for physicalproperties after natural aging at room temperature (about 23° C.) andhumidity (about 50% relative humidity).

More specifically, the basesheet was made from a stratified fiberfurnish containing a center layer of fibers positioned between two outerlayers of fibers. Both outer layers of the UCTAD basesheet contained100% northern softwood kraft pulp and about 3.5 kilograms (kg)/metricton (Mton) of dry fiber of a debonding agent, ProSoft® TQ1003 (Hercules,Inc.). Combined, the outer layers comprised 50% of the total fiberweight of the sheet (25% in each layer). The center layer, whichcomprised 50% of the total fiber weight of the sheet, was also comprisedof northern softwood kraft pulp. The fibers in this layer were alsotreated with 3.5 kg/Mton of ProSoft® TQ1003 debonder.

The machine-chest furnish containing the chemical additives was dilutedto approximately 0.2 percent consistency and delivered to a layeredheadbox. The forming fabric speed was approximately 445 meters perminute. The resulting web was then rush-transferred to a transfer fabric(Voith Fabrics, 807) traveling 15% slower than the forming fabric usinga vacuum box to assist the transfer. At a second vacuum-assistedtransfer, the web was transferred and wet-molded onto the throughdryingfabric (Voith Fabrics, t1203-8). The web was dried with athrough-air-dryer resulting in a basesheet with an air-dry basis weightof approximately 45 grams per square meter (gsm).

The resulting sheet was fed to a gravure printing line, similar to thatshown in FIG. 1, traveling at about 200 feet per minute (61 meters perminute) where a latex binder was printed onto the surface of the sheet.The first side of the sheet was printed with a bonding formulation usingdirect rotogravure printing. Then the printed web passed over a heatedroll with a surface temperature of approximately 104° C. to evaporatewater. Next, the second side of the sheet was printed with the bondingformulation using a second direct rotogravure printer. The sheet wasthen pressed against and doctored off a rotating drum, which had asurface temperature of approximately 104° C. Finally the sheet wascooled by passing room temperature air through the sheet prior towinding into a roll. The temperature of the wound roll was measured tobe approximately 24° C.

The bonding formulation for this example was prepared as two separatemixtures, called the “latex” and “reactant”. The “latex” materialcontained the epoxy-reactive polymer and the “reactant” was theepoxy-functional polymer. Each mixture was made up independently andthen combined together prior to use. After the latex and reactantmixtures were combined, the appropriate amount of “thickener” (Natrosolsolution) was added to adjust viscosity. The “latex” and “reactant”mixtures contained the following ingredients, listed in their order ofaddition.

Latex 1. Airflex ®426 (62.7% solids) 34,200 g 2. Defoamer (Nalco 7565)205 g 3. Water 6,105 g 4. LiCl solution tracer (10% solids) 206 gReactant 1. Kymene ® 2064 (20% solids) 5,420 g 2. Water 10,010 g 3. NaOH(10% solution) 2,800 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture.

Thickener 1. Natrosol 250MR, Hercules (2% solids) 1,650 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer(epoxy-reactive polymer) was about 5%.

The viscosity of the print fluid was 125 cps, when measured at roomtemperature using a viscometer (Brookfield® Synchro-lectric viscometerModel RVT, Brookfield Engineering Laboratories Inc. Stoughton, Mass.)with a #1 spindle operating at 20 rpm. The oven-dry solids of the printfluid was 38.1 weight percent. The print fluid pH was 5.0.

Thereafter the print/print/creped sheet was removed from the roll andtested for basis weight, tensile strength and sheet blocking.

Example 15 Low Blocking 5% Kymene 2064, 10% Glyoxal

A single-ply bonded sheet was produced as described in Example 14, butusing a binder recipe which was designed to reduce blocking in thefinished roll. The ingredients of the “latex”, “reactant”,“anti-blocking additive” and “thickener” are listed below.

Latex 1. Airflex ®426 (62.7% solids) 6,772 g 2. Defoamer (Nalco 7565) 41g 3. Water 1,209 g 4. LiCl solution tracer (10% solids) 41 g Reactant 1.Kymene ® 2064 (20% solids) 1,073 g 2. Water 1,982 g 3. NaOH (10%solution) 544 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture. The anti-blocking additive was added next, followed by thethickener to achieve desired viscosity.

Anti-Blocking Additive 1. Glyoxal (40%) 1,096 g Thickener 1. Natrosol250MR, Hercules (2% solids) 326 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer wasabout 5.0% and the weight percent ratio of glyoxal based on carboxylicacid-functional polymer was about 10%. The viscosity of the print fluidwas 98 cps, when measured at room temperature using a viscometer(Brookfield® Synchro-lectric viscometer Model RVT, BrookfieldEngineering Laboratories Inc. Stoughton, Mass.) with a #1 spindleoperating at 20 rpm. The print fluid pH was 4.9.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and sheet blocking.

Example 16 Low Blocking: 5% Kymene 2064, 20% Glyoxal

A single-ply bonded sheet was produced as described in Example 14, butusing a binder recipe which was designed to reduce blocking in thefinished roll. The ingredients of the “latex”, “reactant”,“anti-blocking additive” and “thickener” are listed below.

Latex 1. Airflex ®426 (62.7% solids) 6,292 g 2. Defoamer (Nalco 7565) 40g 3. Water 956 g 4. LiCl solution tracer (10% solids) 40 g Reactant 1.Kymene ® 2064 (20% solids) 997 g 2. Water 1,842 g 3. NaOH (10% solution)505 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture. The anti-blocking additive was added next, followed by thethickener to achieve desired viscosity.

Anti-Blocking Additive 1. Glyoxal (40%) 1,950 g Thickener 1. Natrosol250MR, Hercules (2% solids) 304 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer wasabout 5.0% and the weight percent ratio of glyoxal based on carboxylicacid-functional polymer was about 20%. The viscosity of the print fluidwas 95 cps, when measured at room temperature using a viscometer(Brookfield® Synchro-lectric viscometer Model RVT, BrookfieldEngineering Laboratories Inc. Stoughton, Mass.) with a #1 spindleoperating at 20 rpm. The print fluid pH was 4.8.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and sheet blocking.

Example 17 Low Blocking: 10% Kymene 2064, 10% Glyoxal

A single-ply bonded sheet was produced as described in Example 14, butusing a binder recipe which was designed to reduce blocking in thefinished roll. The ingredients of the “latex”, “reactant”,“anti-blocking additive” and “thickener” are listed below.

Latex 1. Airflex ®426 (62.7% solids) 17,200 g 2. Defoamer (Nalco 7565)100 g 3. Water 0 g 4. LiCl solution tracer (10% solids) 100 gReactant 1. Kymene ® 2064 (20% solids) 5,475 g 2. Water 8,000 g 3. NaOH(10% solution) 2,800 g

When the NaOH had been added, the pH of the reactant mixture wasapproximately 12. After all reactant ingredients were added, the mixturewas allowed to mix for at least 15 minutes prior to adding to the latexmixture. The anti-blocking additive was added next, followed by thethickener to achieve desired viscosity.

Anti-Blocking Additive 1. Glyoxal (40%) 2,715 g Thickener 1. Natrosol250MR, Hercules (2% solids) 0 g

After all ingredients had been added, the print fluid was allowed to mixfor approximately 5-30 minutes prior to use in the gravure printingoperation. For this bonding formulation, the weight percent ratio ofepoxy-functional polymer based on carboxylic acid-functional polymer wasabout 10% and the weight percent ratio of glyoxal based on carboxylicacid-functional polymer was about 10%. The viscosity of the print fluidwas 120 cps, when measured at room temperature using a viscometer(Brookfield® Synchro-lectric viscometer Model RVT, BrookfieldEngineering Laboratories Inc. Stoughton, Mass.) with a #1 spindleoperating at 20 rpm. The print fluid pH was 5.2.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and sheet blocking.

Example 18 Low Blocking: 10% Kymene 2064, 10% Glyoxal, 10% Wax in FirstPrint Station

A single-ply bonded sheet was produced as described in Example 17, butusing a binder recipe which included an additional anti-blockingadditive in the first print fluid. The additional anti-blocking additivewas a microcrystalline wax, Michem® Emulsion 48040 (sold by Michelman,Inc., Cincinnati, Ohio). Michem Emulsion 48040 is a 40% actives,nonionic emulsion of microcrystalline wax. The wax has a melt point of88° C. For purposes of reducing blocking, the wax was only added to thefirst printed side of the basesheet. The wax was added at an additionlevel of about 10% based on the weight of the latex polymer in the firstprint fluid. The print fluid for the second printed side was identicalto that described in Example 17.

The resulting single-ply bonded sheet was tested for tensile strength,basis weight and sheet blocking. Testing was conducted after 15 days ofnatural aging.

Table 3 shows the testing results of tensile strength, basis weight andblocking measurements for Examples 14-18.

TABLE 3 CD Wet Tensile Basis MD Tensile MD Stretch CD Tensile CD (water)CD Wet/Dry Weight Example g/76.2 mm % g/76.2 mm Stretch % g/76.2 mm (%)Blocking (g) (gsm) 14 1667 45.9 1305 18.5 637 48 25.1 57.0 Control 151649 40.5 1257 16.9 725 58 17.6 56.2 16 1652 42.6 1214 15.5 639 53 15.056.8 17 1614 33.7 1210 15.4 777 64 6.6 55.1 18 1396 38.4 1196 14.2 82069 4.3 56.7

From Table 3, it can be seen that the addition of anti-blockingadditives to the print fluid (Examples 15-18) significantly reduced themeasured blocking value versus the control code (Example 14). Other keysheet attributes were either maintained or improved, such as CD wettensile strength.

In the interests of brevity and conciseness, any ranges of values setforth in this specification are to be construed as written descriptionsupport for claims reciting any sub-ranges having endpoints which arewhole number values within the specified range in question. By way of ahypothetical illustrative example, a disclosure in this specification ofa range of 1-5 shall be considered to support claims to any of thefollowing sub-ranges: 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.

It will be appreciated that the foregoing examples, given for purposesof illustration, are not to be construed as limiting the scope of thisinvention, which is defined by the following claims and all equivalentsthereto.

1. A method of increasing the strength of a fibrous web comprising: (a)adding alkali to an aqueous emulsion of a water-soluble epoxy-functionalpolymer, whereby the pH of the emulsion is raised to about 11 orgreater; (b) mixing the emulsion of the water-soluble epoxy-functionalpolymer with an epoxy-reactive polymer to form an aqueous bindercomposition, wherein the amount of the epoxy-functional polymer relativeto the amount of the epoxy-reactive polymer is from about 0.5 to about25 weight percent on a solids basis; (c) topically applying the aqueousbinder composition to one or both outer surfaces of the web, wherein theelapsed time between mixing the epoxy-functional polymer with theepoxy-reactive polymer and applying the resulting binder composition tothe web is about a day or less; and (d) curing the aqueous bindercomposition on the web.
 2. The method of claim 1 wherein the aqueousbinder composition is cured at a temperature of 120° C. or less.
 3. Themethod of claim 1 wherein the aqueous binder composition is cured at atemperature of 100° C. or less.
 4. The method of claim 1 wherein theaqueous binder composition is cured at a temperature of 40° C. or less.5. The method of claim 1 wherein the aqueous binder composition is curedat a temperature of from about 20 to about 120° C.
 6. The method ofclaim 1 wherein the aqueous binder composition is cured without theemission of formaldehyde.
 7. The method of claim 1 wherein the elapsedtime is about 12 hours or less.
 8. The method of claim 1 wherein theelapsed time is about 3 hours or less.
 9. The method of claim 1 whereinthe elapsed time is about 30 minutes or less.